The following description is provided to assist the understanding of the reader. None of the information provided or references cited is admitted to be prior art to the present invention.
Lithium-ion batteries for electric and hybrid vehicles (for example refer to: Battery Test Manual for Plug-in Hybrid Electric Vehicles; Prepared for the U.S. Department of Energy: Idaho National Laboratory, March 2008) require large electrode capacities and long durability. Development of new anode materials with higher capacity has been one focus of the research.
In lithium-ion secondary batteries, a carbon material such as non-graphitizable carbon or graphite, shows a relatively high capacity (372 mAhg−1) and good cycle characteristics. However, the demand for higher energy density and other characteristics has led to further research in increasing the capacity of the anode beyond that of graphite.
Significant work has been carried out on non-carbon based anodes such as those based upon metal alloys, and intermetallics. In the case of metal alloys, the metal is electrochemically alloyed with lithium, and the resulting alloy is then susceptible to reversible lithium insertion and de-insertion in a battery environment. High capacity anodes using a SnCoC (tin-cobalt-carbon) alloy have been developed (for example, refer to U.S. Pat. No. 2009/0075173). However, Sn alloys (e.g. Sn3Co3C4, where the 3, 3, and 4 represent molar ratios and in some examples may be expressed as Sn30Co30C40) have a theoretically limited capacity of about 728 mAh/g, and a practical capacity of less than 400 mAh/g. In the SnCoC alloys, the tin and carbon are the active materials and the cobalt plays a role in buffering volume expansion of an electrochemical cell during the lithium insertion and de-insertion processes. In terms of capacity, the incorporation of a small amount of silicon, which has a theoretical maximum capacity of 4200 mAhg−1 (refer to: K. Amezawa, N. Yamamoto, Y. Tomii and Y. Ito, J. Electrochem. Soc., 1998, 145, 2751), can increase the capacity, but the amount of silicon which may be added, is limited due the large volume expansion and the poor cycleability. Silicon oxides SiOx, such as SiO, SiO2, or carbon-coated SiO2 are known to deliver a high capacity, but like silicon, these materials can crack easily due to volume changes during charging and discharging cycles. As a result, active material particles can be electronically isolated, thereby decreasing the battery capacity and cycle-life.